Quadrature operators for a harmonic oscillator have the property that they can be measured in a quantum non-demolition way, that is with a precision only limited by the measurement apparatus. This property makes quadrature measurements relevant in quantum sensing, where small signals acting on the harmonic oscillator can be detected by monitoring a quadrature. A topic closely related to quadrature measurements is that of squeezed states, which have reduced uncertainty in one quadrature. Squeezed states are important for enabling quantum sensing and for quantum information and optics in general.
In our recent preprint, we discuss a method to implement quadrature measurements and generate squeezed states. This method is versatile due to the fact that it relies on using a qubit as a detector, an elementary resource available in many physical implementations. This method has promising prospects for experimental implementation with either nanomechamical or electrical resonators.
Our paper, Ultrastrong coupling of a single artificial atom to an electromagnetic continuum in the nonperturbative regime, was accepted in Nature Physics and has appeared as an advanced online publication on October 10, 2016. A News and Views article by Kater Murch discusses our result and two related papers on superconducting artificial atoms in interaction with a cavity and a photonic crystal respectively. See also this news article discussing this result. Congratulations to Pol and the others for this work!
Our paper, on a new method for gate optimization – Floquet Interference Efficient Suppression of Transitions in the Adiabatic basis (FIESTA), was recently published in Physical Review A.
We posted a new paper on the arxiv (http://arxiv.org/abs/1605.08826), presenting a new quantum control method that we named FIESTA (Floquet Interference Efficient Suppression of Transitions in the Adiabatic basis). This work addresses the implementation of quantum gates with a speed approaching the qubit transition frequency. This is the highest possible speed for quantum control of a qubit and reaching it allows for high fidelity gates, overcoming the effect of decoherence.
A new paper on decoherence of flux qubits, by Jean-Luc Orgiazzi et al., has been published in Physical Review B. This paper presents a systematic study of decoherence of flux qubits coupled to a superconducting resonator, which is a building block for a scalable architecture for superconducting quantum information processing.
A new paper is now on the arxiv
Ultrastrong coupling of a single artificial atom to an electromagnetic continuum
Pol Forn-Diaz et al. have observed signatures of ultrastrong coupling between a superconducting flux qubit and the electromagnetic continuum of a one-dimensional waveguide, a transmission line. This work opens the door to study a new regime of quantum optics of single emitters in free space.
The figure below shows the evolution of the qubit spectrum as coupling is increased, with the linewidth growing beyond the qubit frequency, a signature of ultrastrong coupling.
On October 27th, Feiruo succesfully defended his MSc thesis on protected superconducting circuits. Congratulations Feiruo!
Chunqing Deng’s paper titled “Observation of Floquet States in a Strongly Driven Artificial Atom” has been published this week in Physical Review Letters. Congratulations Chunqing!
Here is a link to the paper.
A new paper has been posted on the Arxiv titled
“Observation of Floquet states in a strongly driven artificial atom”
Chunqing Deng and coauthors study the dynamics of a driven flux qubit with driving frequencies higher than the qubit splitting itself. This huge driving field modifies the system in a way that a Floquet description is required, as can be seen in the adjacent figure from the paper.
The latest publication by Mustafa Bal et al., titled
“Dynamics of parametric fluctuations induced by quasiparticle tunneling in superconducting flux qubits”
has been published on PRB 91, 195434 (2015).
These results demonstrate the importance of considering quasiparticles as a source of decoherence in flux qubits.